Function parseInsertableFragment

packages/sdk/src/engine/mutate.ts:680–688

* Parse an HTML fragment in the target document and return its single root * element, or null when it is empty, multi-root, or contains a . * The dispatch path skips validateOp, so these guards are re-enforced here: * never insert raw , never silently drop extra roots.

(document: Document, html: string)

 * never insert raw <script>, never silently drop extra roots.
 */
function parseInsertableFragment(document: Document, html: string): Element | null {
  // Same temp-div approach as apply-patches.ts to avoid cross-document issues.
  const tmp = document.createElement("div");
  tmp.innerHTML = html;
  if (tmp.querySelector("script")) return null;
  const node = tmp.firstElementChild;
  if (!node || node.nextElementSibling) return null;
  return node;
}

function handleAddElement(
  parsed: ParsedDocument,